This invention relates in general to vehicle wheels and in particular to an apparatus for measuring axial deviation of a vehicle wheel surface relative to a reference plane.
Vehicle wheels typically include an annular wheel rim and a circular wheel disc. The wheel disc can be formed across the outboard end of the wheel rim or recessed within the wheel rim. The wheel rim is adapted to carry a pneumatically inflated fire. The wheel rim has inboard and outboard tire retaining flanges formed on the ends thereof which extend in an outward radial direction to retain the tire on the wheel. Inboard and outboard tire bead seats are formed on the outer surface of the wheel rim adjacent to the corresponding tire retaining flange to support the fire walls and form an air-tight seal therewith. The wheel rim also includes a reduced diameter drop well between the tire bead seats to facilitate mounting the fire upon the wheel.
The wheel disc includes a central wheel hub for mounting the wheel upon a vehicle. The inboard face of the wheel hub is typically machined to form it flat surface to assure good contact between the wheel and the vehicle. A pilot hole and a plurality of wheel stud holes extend through the wheel hub. The pilot hole is centered on the hub and the stud holes are spaced equally about a circle which is concentric with the pilot hole. The pilot hole can receive the end of an axle while the wheel stud holes receive wheel studs for attaching the wheel to a vehicle. The wheel disc also typically includes a plurality of wheel spokes which extend radially from the wheel hub to the wheel rim and support the hub within the rim.
Vehicle wheels can be cast in a single piece from a light weight metal such as aluminum, magnesium or titanium, or an alloy of a light weight metal. Such wheels are becoming increasingly popular because they weigh less than conventional steel wheels and can include outboard wheel disc faces which are formed in a pleasing atheistic shape. One piece wheel castings are usually formed by a gravity or low pressure casting process. The wheel castings are finished by machining to a final shape.
Two separate machining operations are typically used to finish a wheel casting. Referring now to the drawings, a wheel finishing process with two machining operations is illustrated in the flow chart shown in FIG. 1. In functional block 10, the outboard end of a rough wheel casting is clamped to the face of a wheel lathe for the first machining operation. A wheel lathe is a dedicated machine designed to finish wheels. Wheel lathes typically include a plurality of cutting tools and are operated under computer numerical control (CNC) to perform a number of related machining operations. For example, a wheel lathe can be equipped with a taming tool, a facing tool and a drill bit and be programmed to sequentially ram, face and bore a wheel casting. The wheel lathe face typically includes a plurality of jaws which grip the outboard wheel retaining flange and tire bead seat. Consequently, the outboard wheel rim end is not finished during the first machining operation.
The outside and inside surfaces of the wheel rim are turned to their final shapes and the inboard surface of the wheel hub is faced in functional block 11. Additionally, the inboard end of the wheel rim is finished. The partially finished wheel casting is removed from the wheel lathe, reversed and clamped on another wheel lathe for a second machining operation in functional block 12. During the second machining operation, the inboard wheel flange and fire bead seat are gripped by the wheel lathe jaws, exposing the outboard surface of the wheel disc and the outboard end of the wheel rim for machining.
After clamping the wheel on the lathe, an axial distance between a portion of the surface of the outboard wheel casting face and a reference plane is measured in functional block 13. The reference plane is defined by a finished surface on the wheel, such as the inboard end of the wheel rim. The measured axial distance is compared to a desired axial distance to determine an axial deviation for the wheel casting outboard face.
It is necessary to determine the axial deviation of the outboard wheel face in functional block 13 because the axial dimensions of castings can vary from wheel to wheel. The variation of the axial dimensions can be the result of slight deformations of the wheel castings which can occur as the castings are pulled from the wheel mold. Additionally, metal shrinkage can cause variation in the thickness of portions of the wheel discs. Thus, it is not sufficient to finish the outboard wheel face by simply following the surface contour of the wheel casting face during the second machining operation. Doing so can result in cosmetic differences between the appearance of finished wheels and/or undesirable fitment of wheel trim pieces. For example, variation of the axial dimensions of the hubcap retention area may cause hubcaps, which are intended to be flush with the wheel face surface, to be recessed when mounted upon some of the finished wheels. Alternately, the variation may cause the hubcaps to extend above the wheel face surface.
Accordingly, it is known to determine the axial deviation between an axial dimension of a critical portion of the outboard surface of the wheel disc casting and a corresponding surface on a desired finished wheel surface. This axial deviation is used to determine the amount of metal to be removed during the second machining operation to assure that the finished wheel surface is within tolerances of the desired wheel surface.
It also is known to include mechanical or electronic probes on a wheel lathe to measure the axial distance between the face of the wheel casting and the reference plane while the wheel casting is clamped on the lathe. The measurement can be made before starting the second machining operation, as shown in the flow chart, or the lathe can be stopped during the second machining operation for the measurement. In either case, a series of probe readings of points located on the critical portion of the wheel face are taken. For example, if the fit of hubcaps is a concern, the axial variation of the surface of the hubcap retention area is determined. First, a series of points surrounding the pilot hole are measured. Because only a single probe is typically available, the wheel is indexed to align each of the points with the probe. At least three data points are measured to define the surface which is critical to proper machining of the wheel. The data points are used to define actual axial distances between the surface points and the reference plane. The differences between the actual axial distances and corresponding desired axial distances are combined to provide an axial deviation.
In functional block 14, the second machining operation turns and faces the outboard wheel face. During this operation, the outboard tire retaining flange and the outboard tire bead seat also are mined to final shapes. The surface of the hubcap retention area is machined to final shape and the stud mounting holes are drilled through the hub in functional block 15. Alternately, the wheel casting may be removed from the wheel lathe and the drilling operation completed at another work station.